This is a big deal.

British National Party (BNP, a far-right nationalist party) membership and contacts list. 12,801 individuals are represented. Contains contact details and notes on selected party members and (possibly) other individuals. The list has been independently verified by Wikileaks staff as predominantly containing current or ex-BNP members, however other individuals who have donated to the BNP or who have had other contact (not necessarily supportive) with the BNP or one of its fronts may also be represented.

Says BBC:

Occupations ascribed to the listed names include teachers, a doctor, nurse, vicar and members of the armed forces.

While there is no ban on many of those professions joining the BNP, its right-wing political stance and whites-only membership policy are seen by many as incompatible with frontline public service.

Police officers, on the other hand, are formally banned from joining, a policy which is recognised in the list.

Alongside the name of a serving officer, the document states that there is "Discretion required re. employment concerns".

Seems that the BNP database wasn't hacked from the outside, but that someone on the inside leaked the list.

There's a lot more leaked BNP documents on the Wikileaks website.